Many a fan of local Latin pop band Rock'n Son have heard tunes in the group's repertoire played by other musicians. That's because the band's keyboardist and writer, Raul del Sol, still has a soft spot for songs he has peddled to other artists. During Rock'n Son's live sets, which begin at 10:00 Thursday evenings at Starfish, you might hear ballads like "Encuentro" and "Diferencias," both recorded on Spanish-language rocker Amaury Gutierrez's latest album. Francisco Cespedes, Chayanne, and even Jamaican pop sensation Beenie Man also have tapped del Sol's gifts for composition and arrangement. While love often is del Sol's subject, his music recalls the confections of the troubadour-style Cuban nueva trova movement of the Sixties. He writes polished, apolitical folk rock with a tropical feel.